March 1, 2008 Water Supply Forecast Summary

March 1, 2008 Water Supply Forecast Summary

Date: March 10, 2008

Subject: March 1, 2008 Western Snowpack Conditions and Water Supply Forecasts

The following information is provided for your use in describing western climate and water supply conditions as of March 1, 2008.

OVERVIEW

Western snowpack is near or above average across most states. Changes since February 1 are also up except from record levels over the Coastal Ranges in OR and WA. Other decreases in the Oregon Cascades and southwest NM are noteworthy.

During the past month, the spring and summer streamflow forecasts are near or above average in all but the Northern Rockies (WY), Eastern Slope of MT, the Snake River Basin (ID), and south central NM. No changes since the February 1 forecasts dominate across about half the West but increase flows are now forecasted for Colorado, the Northern Rockies (MT & ID) and the Great Basin (NV, ID, & OR). Flows are forecasted to decrease from near record forecast volumes over central Arizona.

Only Arizona’s reservoirs are averaging above normal followed closely by Colorado which is near average. The remaining states are below the long-term average.

SNOWPACK

On March 1, 2008, the western snowpack is above average compared to the long-term climate statistics across the Cascades, Central and Southern Sierra, and 4-Corner States (except southern New Mexico) (Fig. 1). Values are down over eastern Alaska and to a lesser degree over central Wyoming. During the past month, snowpack is down from near record depths over Oregon Coastal Ranges and down over the eastern slope of the Oregon Cascades and southwest New Mexico (Fig. 2). Other areas with decreased snowpack are scattered across the Intermountain West (Idaho), south central Colorado, and northern California.

A map containing a daily update of the westwide snowpack may be obtained from the following URL - http://www.wcc.nrcs.usda.gov/gis/snow.html

SEASONAL PRECIPITATION

Preliminary seasonal precipitation is above normal, (110% of average) from southern California, across the 4-Corners States, into portions of the Northern Rockies as shown in Fig. 3. Although the Pacific Northwest isn’t available yet, it will eventually show northern Idaho with above normal values but scattered above to below totals across the remaining areas. Values are under 50% of the long-term average over much of southeast Interior and the northern Panhandle of Alaska.

Monthly and seasonal precipitation maps are available from the following location - http://www.wcc.nrcs.usda.gov/gis/precip.html and http://www.cbrfc.noaa.gov/wsup/westwide/westwide.cgi

SPRING AND SUMMER STREAMFLOW FORECASTS

Despite La Nina’s typical drier weather, forecast issued 1 March shows well above normal volumes over much of the 4-Corners States. Above average flows are expected over the Cascades and Great Basin (Nevada) (Fig. 4). Areas with lower expected flows are forecasted for the Snake River Basin (Idaho), Green, Sweetwater, and Powder-Tongue Basins in Wyoming, Upper Columbia River (Washington & British Columbia), the eastern slope of the Montana Rockies, and portions of southern New Mexico. Forecast changes since last month include significant decreases over central Arizona, and extreme southwest New Mexico, and to a lesser extreme over the Power-Tongue in Wyoming and Montana (Fig. 5). Forecasts are up significantly (>15%) near the 4-Corners and the Front Range of Colorado and New Mexico.

Specific state streamflow summaries can be obtained from the Internet location - http://www.wcc.nrcs.usda.gov/cgibin/bor.pl

RESERVOIR STORAGE

As of March 1, 2008, reservoir storages, shown in Fig. 6, are above seasonal averages in only Arizona and near average in Colorado. Reservoir storage is below average in the remainder of the Western States and especially noteworthy in Wyoming, Utah, Oregon, and Nevada.

FOR MORE INFORMATION

The National Water and Climate Center Homepage provides the latest available snowpack and water supply information. Please visit us at http://www.wcc.nrcs.usda.gov

/s/ NOLLER HERBERT

Director, Conservation Engineering Division

March 10, 2008 Page 7 of 8

Fig. 2. Mountain Snowpack Change between 1 February and 1 March 2008.

ftp://ftp.wcc.nrcs.usda.gov/support/water/westwide/snowpack/wy2008/difsnow0803.gif.

Fig. 4. Water Supply Forecasts - March 1, 2008.

ftp://ftp.wcc.nrcs.usda.gov/support/water/westwide/streamflow/wy2008/strm0803.gif

Fig. 5. Change in streamflow forecast between 1 February and 1 March 2008.

ftp://ftp.wcc.nrcs.usda.gov/support/water/westwide/streamflow/wy2008/difstrm0803.gif.

March 10, 2008 Page 7 of 8